if we get to masjid and we find out that jamat is over..can few brother make thier own jamat in the back of masjid?
It is Makrooh to make a second Jamaat in a proper Musjid after the first Jamaat. If a few brothers missed the Jamaat, then they should perform their Salaat individually without any Adhaan or Iqaamat. (Fataawa Rahimiyah vol.4 pg.134)
However, Jamaat can be made in the Sehn of the Musjid or in a Musallah (not proper Musjid).
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai